During semiconductor wafer fabrication, light can be utilized in a lithographic process to enable transfer of very small lithographic patterns, such as nanometer-scale lithographic patterns, from a lithographic mask to a semiconductor wafer. In a common lithographic process, for example, light from a lithographic light source is used to transfer a pattern formed on a lithographic mask, to a semiconductor wafer, by exposing a layer of resist formed over the semiconductor wafer to emitted light that has been reflected from the lithographic mask.
A conventional approach to evaluating the suitability of a resist in semiconductor wafer fabrication involves the use of scatterometry as a post hoc metrology procedure, performed after development of a transferred lithographic pattern. Typically, light from a scatterometry light source is scattered from the surface of a patterned semiconductor wafer, and the wavelength and polarization of that scattered light are compared to unscattered light from the same source. Changes observed in the scattered light correspond in a predictable way to characteristics of the developed lithographic pattern. In this way scatterometry is conventionally used to confirm the dimensions of a transferred lithographic pattern.
By performing scatterometry measurements late in the process, e.g. after development of the resist pattern, conventional techniques often result in an unnecessary consumption of resources used in the intervening fabrication steps, when it is discovered that, for example, due to poor characteristics of resist, a desired high resolution pattern has not been properly formed.